1. Field of the Invention
The present invention pertains to improving or maximizing fuel efficiency for vehicles that use an internal combustion engine for power.
2. Description of the Related Art
There are many motivations for improving fuel economy of road vehicles (and other vehicles). Transportation represents a significant portion of global energy use. In the United States, for example, the EPA estimates that transportation accounts for approximately twenty five percent of all energy use. Vehicles that consume more fuel emit more greenhouse gases and contribute more significantly to global warming. Given the rapid depletion and increasing scarcity of fossil fuels, gas prices have historically been rising. Gas prices are bound to rise even more substantially in the future. With high fuel prices, more and more consumers will find fuel efficient vehicles desirable for their budget. Society therefore urgently seeks to improve fuel economy. It will become more and more urgent, as evidenced by the passing of the national fleet mileage rule under President Obama.
Of all the components of a typical car that play a role in fuel economy, the vehicle's engine is the most influential factor. As the only source of power for the typical (nonhybrid and nonelectric) automobile, the efficiency of the engine ultimately limits the fuel efficiency of the vehicle.
For many years, vehicles and engines have constantly undergone redesign with fuel efficiency in mind. Yet, in the thirty six years since the first oil crisis in 1973, the fuel economy for comparable vehicles relying solely on internal combustion engines for power has not gone up by a significant amount. Although the typical engine has undeniably been improved in design and performance, there remains a trade-off between vehicle performance and fuel economy. Overall vehicle performance has increased at the cost of fuel economy. To achieve better acceleration and comfort, and/or to carry heavier loads, bigger engines with higher outputs are needed. However, bigger engines also consume more fuel. Compact cars have been known to achieve excellent fuel economy, but they are also unable to fulfill the needs that are met by large sedans, SUVs and trucks, which have relatively poor fuel economy.
As engine conditions (i.e. load and RPM) vary, the efficiency of the engine (amount of work done per unit of fuel consumed) can change dramatically. The typical internal combustion engine used in automobiles operates most efficiently around approximately sixty percent of the maximum engine power output at a certain speed. The most efficient region of operation varies from engine to engine. Consider the fact that the typical mid-size sedan has around 150 peak hp, while maintaining highway speeds only requires the engine to output 30 hp, only about twenty percent of maximum engine power. While maintaining city or local speeds, the engine of the typical mid-size sedan uses even less power, and an even smaller portion of maximum power. This means that under typical driving conditions, with the driver's foot continuously on the throttle to maintain the vehicle at approximately the same speed, the engine is operating at a low percentage of its maximum power, and not in a fuel efficient region.
With conventional driving methods, the engine runs under low power (and efficiency) most of the time, with an increase in power and in efficiency only at certain short moments such as when accelerating from a stop or to pass another vehicle. Accordingly, for the majority of the time the typical driver drives the vehicle under conditions that make the engine use fuel relatively inefficiently. Conventional wisdom is to maintain a level speed, avoid acceleration, avoid “jack-rabbit” starts and stops, and if one has to accelerate, to accelerate as smoothly and gently as possible to save fuel. However, this conventional driving method results in fuel efficiency that falls well short of the vehicle's potential fuel economy because this conventional method only uses a small percentage of engine's maximum power output.
Compact cars, with their smaller engines, are more fuel efficient precisely because smaller engines output less maximum power and produce poorer acceleration. Therefore, under normal driving conditions, the driver already uses the engine closer to its optimal efficiency region for a larger proportion of the time than if he or she were to drive a vehicle with a larger engine, such as an SUV.
To increase fuel economy, industry specialists have focused almost exclusively on how to make more use of the engine's most fuel efficient operating region, or “sweet spot”, under normal driving conditions. For example, manufacturers have come up with a way to make vehicles that can run with only half of its cylinders working (U.S. Pat. No. 4,383,514 to Fiala). Thus, a six cylinder engine could shut off half of its cylinders, and run its other three cylinders at higher efficiency to accomplish the same amount of work using less fuel than running all six cylinders under a lower percentage of maximum power (lower efficiency). The benefit of this approach is that the vehicle can still reap the performance benefits of having a bigger engine for bursts of acceleration, while for times when less acceleration is needed the vehicle uses an effectively smaller engine running in a more efficient state to do the work. This approach in engine design is particularly effective for larger vehicles. However, there is still no guarantee that the engine will operate near or at peak efficiency and certainly not anywhere near all the time. There is only an increased efficiency that may be reached and not an optimal efficiency.
Hybrids are currently the most effective method to improve fuel economy. It is possible for a hybrid's engine (using combustion) to stay in the most efficient region much of the time. Hybrids may use a small engine (combustion) that is turned off at low speeds when the engine will not be able to run in the most efficient region, when the motor (electric) is used instead. When the engine is used, it is started and fixed in an efficient state, with adjustments made to motor power to handle varying load conditions. For example, if the engine running in the sweet spot does not provide enough power, the motor can be used to supplement the power needed to drive the vehicle. By contrast, if the engine running in the efficient state provides more power than is needed, the motor can be used to turn the excess portion of the power the engine produces into electricity that is then stored in the batteries for the motor to use. Thus the engine in a hybrid is either on and operating in and efficient state or not turned on at all. This characteristic gives the hybrid superior fuel economy. However, the extra motor and batteries as well as a more complex controller add to the cost of producing a hybrid vehicle. The hybrid is an expensive answer to the need for better fuel economy. Moreover, it does not improve efficiency of the millions of fossil fuel burning vehicles on the road.
Another approach, which does not require car or engine redesign, is to have drivers alter their driving styles to try to use the vehicle's engine in a fuel efficient state as much as possible. There are many methods of providing feedback to a driver to indicate or suggest what he or she must do to improve fuel economy.
U.S. Pat. No. 7,512,477 to Quigley et al. discloses an engine management system that takes in the engine's current operating parameters and compares the engine's current operation to a speed-torque map, then generates a display for a driver or some other engine operator. The goal is to guide the operator to use the engine efficiently with the help of the predetermined and stored speed-torque map. Because the speed-torque map, also known as a BSFC diagram, will have different characteristics depending on the engine, the map loaded into Quigley's engine management system (EMS) would have to be specific to the particular engine in the vehicle in order for the driver to hit the efficient region of operation with the EMS. The EMS described by Quigley et al. is capable of directing the driver to use the engine's “sweet spot” but does not necessarily lead to better fuel economy over time, because the driver cannot maintain the engine in the “sweet spot” anywhere near all the time.
Generally, to run the engine in the sweet spot, less fuel is used for each unit of work done, but more fuel is consumed per unit of time than what is generally needed to maintain the vehicle's current speed. In other words, to achieve what would be the greatest fuel efficiency, the vehicle has to accelerate. The consequence of this is that the excess work the engine produces becomes translated into the kinetic energy of the vehicle, which gets higher and higher and results in the vehicle building more and more speed. Quigley et al. provide no way to release this excess energy and let the vehicle return to an appropriate speed unless the throttle is partly released. The moment the throttle is partly released, the engine will no longer be operating in the sweet spot, and the excess energy is partially wasted. Quigley et al. suggest a method of evaluating a driver's performance according to a ratio of distance over which the engine operated in an area of high performance to a predetermined running interval distance, so a score such as fifty percent could be assigned. This evaluation is not equivalent to evaluating fuel economy, because it provides no information on how well or poorly the driver performs while not driving in the sweet spot. Finally, a potential drawback of Quigley et al. is that the driver must pay attention to the display and make the effort to operate the throttle in accordance with the display, which might make driving inconvenient and/or uncomfortable.
In the past, the focus has been to design engines that operate more efficiently under typical driving conditions, or to assist the driver to use engines in the region of the best fuel efficiency. In the case of providing guidance to drivers, however, the present inventors are not aware of any art that has addressed what is to be done after operating the engine in the sweet spot, which generally results in more acceleration than the driver needs or desires.
In order to obtain the best fuel economy over time, the present inventors have determined that it is necessary to take a step back from the engine-centric view, and consider what happens to the vehicle's energy as whole including the excess kinetic energy that the engine produces while operating in an efficient state. This excess kinetic energy must not be allowed to go to waste and must be used to contribute to the distance that the vehicle travels to achieve the best fuel economy. A system or device that is portable and works universally on any automotive vehicle without requiring predetermined information specific to each vehicle or engine is also needed. An automatic and universal system, usable on any vehicle without customization, which is capable of managing not just the engine output, but also the energy of the vehicle as a whole, preferably without inconveniencing the driver, is desired.